Egg – Larva – Pupa – Adult

Their life cycle begins when the adults lay eggs into soil in the spring and early summer. Once hatched the larva burrow into the soil and locate earthworms on which they feed as parasites. During the course of the summer they will grow as a larva and when large enough pupate into the adult fly.

Because they breed outside in the land that contains earthworms treatment of the breeding sites is impossible.

When the temperatures drop in the autumn the adult flies migrate from these summer breeding sites into buildings where they hibernate in attics, windows, cavity walls and any other suitable voids. They cluster in extremely large numbers, sometimes in tens of thousands.

During the early stages of this migration phase they may leave the building on warmer sunny autumnal days before returning at night. Once temperatures are consistently low this migration will cease although this may take several weeks and come in a number of waves.